I bought a used CZ 375 H&H in the spring of'76,
I mean 1976,It had a california style stock,wit a montecarlo sloping forward,Keith style..not the idiot german humpback stock, they make to day,that hits you in the face.
I had bought a cz 458 a few years ago with the horrible stock,and though he shot good groups.I traded it down the river Po immediately,for the sake of my only face.
I have a ruger M77bolt action that shoots very well 458 Lott cast bullets with a gentle and beautiful stock.
Back to the old reliable 375H&H. I kept for some time a N°1 ruger tropical,and sold that too,but I am still crying and regretting.such a mistake.
The post '64 Win 70 has a well deserved fame of extraction failures,Traded that one too,an bought a winchester M1 Garand.( for cast bullet shooting,of course)
Now back to the Old reliable CZ.
Slugging the barrel in modern rifles is meaningless,One of the old wifes tales of CB shooting .the bullet must fit THE THROAT.not the bore.
If throat measuring is as difficult to you as it is to me,load your bullets unsized,or load the fattest bullets that you can chamber in your gun without effort.
My favourite production bullets come from an old RCBS bullet,bought in the late seventies,that cast in WW mike .378 , or a flea's hair more,I pass them in a .379 G&H die,lube all the grooves and seat the gas checks and shoot them at 1400 fps using the slow shotgun powders I can find in Italy.- Around.1.5 MOA.
I use a Neil Jones nech sizing die, just a caress on the neck is enough sizing , I use a 7/8 die in a the Dillon 650 press.
Next stage is lee powder through expanding die with the lee powder measure on top.
The old RCBS bullet seater die was honed up to accept 379 bullets it was made for .375 jackets.and sized down my cast slugs.
A couple of years ago I shot a roe deer at about 80-100 meters from a high tree stand with this rifle and bullet ,loaded around 1600 fps using Vihtavuori 110 powder,he died on its tracks,and we ate up to the bullet's hole.
Absolutely ,no fillers ,and use winchester Large rifle primers or other manifacturer's magnum rifles.
I have recently got an LBT 300 gr moulds 4 cavity,,shot them only once,they are promising.
4 inches at 50 Yards is what you should expect with .375 bullets.If you have little leading,thank the generous charge of fast burning Unique that bumps up your undersize bullets.
Even .377 saeco bullets gave me 1.5 moa at 100 METRS,not Yards. Get 379 to 380 bullets and try them unsized,I think that being your whitetail deer much bigger than European roes ,you shoud try for 1700-1800 fps.
My rifle prefers gas checked bullets.
When I want harder bullets I like to quench frosted bullets directly from the mould,into the cold water.
Putting them into the oven is too much work to me,I put the roast beef & pizza into the oven.